Explicit preffixed namespace in config

Explicit preffixed namespace in config

As described on http://getcomposer.org/doc/04-schema.md#autoload

>Please note namespace declarations should end in \\ to make sure the autoloader responds exactly. For example Foo would match in FooBar so the trailing backslashes solve the problem: Foo\\ and FooBar\\ are distinct.

Without this fix next code throws 'Cannot redeclare Zend_Registry' error
```php
class_exists('\Zend\Registry')
```